How to create a glowing object in a light background?
You will need to have something dark in your image to make the glow work. It needs contrast or it will look washed out. You have made your rings black and you could try to make the nucleus light up those. That could make the nucleus appear to emit light.

Maybe something like this?



Here is the material node setup for the glowy thing in the middle.
It can be applied to any object larger than the falloff radius.
It controls how mush light that should be emitted by the volume by creating a gradient from the objects center and out.